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Abstract:

A reticular tubular structure formed by extruded filaments of synthetic
plastic material extending in two oppositely tilted directions with
respect to an axial direction of the tubular reticular structure. The
filaments cross one another to form a tubular net of interconnected
rhomboid meshes, vertices of the rhomboid meshes being formed by
crossover points between two filaments fused together, while sides of the
rhomboid meshes are formed by said filaments outside the crossover
points. The tubular reticular structure is molecularly oriented in both
longitudinal and transverse directions thereof, and is calendered so that
the crossover points, at the vertices of the rhomboid meshes, and the
filaments, at the sides thereof, have the same common thickness.

Claims:

1. A tubular reticular structure, formed by extruded filaments of
synthetic plastic material extending in two oppositely tilted directions
with respect to an axial direction of the tubular reticular structure,
said filaments crossing one another to form a tubular net of
interconnected rhomboid meshes, vertices of said rhomboid meshes being
formed by crossover points between two filaments fused together, while
sides of said rhomboid meshes are formed by said filaments outside said
crossover points, wherein said tubular reticular structure is molecularly
oriented in both longitudinal and transverse directions thereof, and
wherein said tubular reticular structure is calendered so that said
crossover points, at the vertices of the rhomboid meshes, and said
filaments, at the sides thereof, have the same common thickness.

2. The tubular reticular structure according to claim 1, wherein said
crossover points and said sides of said rhomboid meshes have the same
common thickness along the whole extent of said tubular reticular
structure.

3. The tubular reticular structure according to claim 1, wherein the
plastic material of the reticular tubular structure has the
characteristics of an elastomer.

4. A material with a tubular reticular structure of the type formed by
filaments that cross over one another at crossover points to form a net
mesh, the material being shaped by a process comprising the steps of:
continuously extruding a synthetic plastics material to obtain a tubular
reticular structure in which the crossover points of the filaments are
thicker than the actual sides of said net mesh; continuously subjecting
the extruded tubular reticular structure to a two-dimensional molecular
orientation operation in longitudinal and transverse directions, by
arranging the extruded tubular reticular structure as a rope and
hot-drawing the rope longitudinally to form an oriented tubular reticular
structure; continuously subjecting the oriented tubular reticular
structure arranged as a rope to a transversal drawing and flattening
operation, using a widening device that gives the oriented tubular
reticular structure a flattened configuration in which two parts of the
oriented tubular reticular structure are placed one on top of the other
to form a flattened oriented tubular reticular structure; and
continuously subjecting the flattened oriented tubular reticular
structure, while maintaining the widened and flattened condition thereof,
to an operation to even out the thickness of the flattened oriented
tubular reticular structure, by passing the flattened oriented tubular
reticular structure through a calendering machine that transforms the
flattened oriented tubular reticular structure into a laminated oriented
tubular reticular structure in which the crossover points of the
filaments forming the sides of the net mesh are made to have the same
thickness as the actual sides of the net mesh.

Description:

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method for shaping a material with a
reticular structure, or a net structure, which also includes a plant for
performing same and the reticular material resulting from the method.

[0002] The method in question is applied to handling a synthetic plastics
material with a reticular structure, in particular one having a tubular
shape, which is one of the type with a known constitution and obtained by
means of an extrusion process.

[0003] The reticular material resulting from the said method is
particularly applied to the packaging industry in general, and it is
worth mentioning how important its use is in packaging food products and,
more specifically, fruit and vegetable products.

[0004] For many years the use of net containers has been known, either of
the knotted type, such as net bags, or of the type bound by plain
knitting, such as the bags of a loosely woven fabric, like hemp canvas,
sackcloth, matting, leno, etc. to transport onions, potatoes, etc., on a
commercial level, or of the type obtained by extruding a synthetic
plastics material, such as the one used to make bags for packaging
various products used on a domestic level, such as oranges, potatoes,
onions, nuts, chestnuts, lemons, etc.

[0005] The Spanish Utility Model No. 158.340 is known, which describes an
extruded net that is mono- or biaxially oriented, without this
transcending to the cross points, which has low tensile strength, good
dimensional stability and reduced coverage ability.

[0006] The actual applicant is the owner of Spanish Utility Model Nos.
290.122, 290.123, 290.124, 290.125 and 290.126 that relate to different
variants of tubular flattened extruded net arrangements, made up of two
or three non-molecularly oriented filaments, having the characteristics
of low tensile strength, good dimensional stability and high coverage
ability.

[0007] Patent EP 0 788 974 is also known, which relates to a packaging
made up of non-oriented extruded net which is folded with a plastic film
and joined to it by welding, and Patent ES 2.014.712 which describes
packaging bags made from woven net with plastic filaments which is folded
with a plastic film joined to the woven net by welding.

[0008] Moreover other patents are known that are related to this
application, and they are:

[0009] U.S. Pat. No. 3,140,330 relates to a system for drawing,
longitudinally and transversally, a tubular net after it has been
extruded controlling its drawing with a calibration ring and a hot bath,
with the net being dragged by a winder, not shown, and guided by two
lower submerged rollers, which do not come into contact with one another,
and a top guide roller. In this patent no operation for laminating the
tubular flattened net resulting from the drawing operation, is envisaged.

[0010] U.S. Pat. No. 2,002,711, relating to a method for producing a flat,
continuous and smooth web of cellulosic material, in other words, it is
not a reticular tubular structure, although it envisages using
calendering rollers to surface the web of material. Nevertheless, the
plant shown in said patent to describe the process for producing the
flat, continuous and smooth web is slightly reminiscent of possible,
non-claimed variants described in this invention and which correspond to
FIGS. 13 and 14 in the description.

[0011] U.S. Pat. No. 3,968,621 relates to a method for obtaining a flat
device for transporting cans of drink, which is made up of a plurality of
cables which, describing irregular trajectories on a plane that determine
meetings between pairs of said cables, form a flat grid with openings
slightly smaller than the section of the cans to be contained. This
narrow web which is flat, and therefore not tubular, and is not
molecularly oriented by the corresponding longitudinal drawing and
transversal widening operations, is a different starting material to that
which is the object of this patent application, and it is not to be
understood that this is affected by the fact that in some case said
narrow support web for drink cans undergo a calendering operation, which
is performed by flattening the cables and intersection points until they
are reduced to a perforated lamina that is similar to the equivalent
narrow webs obtained through die-cutting or punching the laminar
material.

[0012] FR patent 1.566.717 relates to a plastic mesh net intended to cover
boxes for transporting fruit and vegetables, which is obtained from a
plastics material that is shaped by extruding a material with a reticular
tubular structure that is subjected to a single longitudinal drawing
operation, without being accompanied at any time by a transversal
widening operation, after which the material with a reticular tubular
structure opens, transformed into a laminar material such as those in
FIG. 1 and A of FIG. 5, with the material in the above-mentioned shape
being subjected to a calendering operation to give it a flat shape.

[0013] U.S. Pat. No. 3,370,116 relates to a method for widening a
reticular tubular structure up to a predetermined size, this aim being
achieved with a mandrel 12, the projection of a hot fluid in station A
and a cooling operation in station B, feeding the material by dragging it
on rollers 18 without this in any way suggesting a laminating effect,
since said rollers 18 do not form a laminating calendering machine.

[0014] Patent EP 0 067 238 relates to a method and apparatus for the
continuous biaxial orientation of an extruded web of plastics material
that is dragged and surfaced by passing through the two rollers 16A and
16B to obtain the longitudinal drawing thereof, which is followed
immediately by a widening operation performed by the widening blades 18,
without this at any time producing a laminating operation of the web,
which undoubtedly does not have a reticular tubular structure.

[0015] Finally, Patent ES 2.023.601 is known, which describes a method for
obtaining an elastic net for carrying loads, as well as the net obtained
therewith.

[0016] Moreover, this section must also consider the application field of
the material that is the object of the invention, the use of which can be
limited, on the one hand, to packaging food products in general and fruit
and vegetables in particular and, on the other hand, to containing loads
stored on pallets.

[0017] With respect to the case of the first application, it is worth
highlighting, owing to their extensive use and good functional
suitability, the packagings made of reticular net and auxiliary printed
elements such as bands of printed film, paper labels, plastic labels,
etc.

[0018] In those packagings that include net and plastic bands, the net may
be of the woven, oriented extruded, or non-oriented extruded type. Each
of these types of net has, for its main function as the element for
containing the product inside the packaging, certain advantages and
disadvantages, namely:

[0019] Woven net has a good strength-weight ratio, which makes it possible
to optimise the cost of the packaging. It also has the advantage that,
because of its light weight and volume, the spools can handle
considerable metres of material at one time, which increases the work
autonomy of automatic packaging machines. The disadvantage of woven net
is that it has very low dimensional stability, and so the packagings
formed using this type of net are easily deformed, which has a negative
effect on the vertical structure and the ability to display the message
or design printed on the packaging.

[0020] The packagings obtained with oriented extruded nets have the same
advantages and disadvantages as those made from woven net, with the added
fact that, generally, oriented extruded nets offer a low product coverage
factor because the oriented threads have a small section.

[0021] From non-oriented extruded nets, packagings that maintain their
vertical structure and provide a clear view of the design printed on the
film bands are obtained. Nevertheless, these nets have a non-too
favourable strength-weight ratio, and so heavyweight net has to be used,
which negatively affects the cost of the packaging. On the other hand,
since its threads are not oriented and they have a substantial section,
these nets have a high product coverage factor, but at the same time, the
spools can only handle a few metres at a time, which causes frequent
stoppages in the automatic packaging machines to replace the empty
spools.

[0022] With respect to the second case of application, reticular
structures or flat nets are used when it is essential that air circulates
inside the palletised load, so as not to produce water vapour, as is the
case of pallets containing boxes of fruit, vegetables or fresh
vegetables; or when hot elements are arranged which are to cool in the
atmosphere, such as bricks and ceramic pieces just after they have been
fired.

[0024] Perforated films have good elasticity and they are not very thick,
and so a high number of metres can be provided on one spool, and they do
not produce loose threads or a large amount of waste when the pallets are
undone. As for the disadvantages, it is worth mentioning that they have
limited tensile strength and that, since to maintain their cohesion the
perforated surface cannot be very high, the ventilation effect inside the
palletised load is very much reduced.

[0025] Extruded nets offer good tensile strength, but they suffer from the
drawback that, owing to their thickness and rigidity, only a few metres
fit on the spool and that the net takes up considerable space when the
pallets are undone, and it has to be placed in waste containers.

[0026] Woven nets do not offer as good a shearing strength as the extruded
oriented ones, particularly when the palletised load has ends with edges,
but their main drawback is that when the net is cut to undo the pallets,
threads come off that accumulate in the wheels and axes of the back
pallet parts and stacking trucks, and that can cause breakdowns or, it at
least means that the cleaning and maintenance frequency of these machines
has to be increased.

BRIEF SUMMARY OF THE INVENTION

[0027] In view of the cited background, the detailed drawbacks of the
tubular nets used to date and the characteristics required for a net made
of synthetic plastics material of the type obtained from extrusion,
depending on the application of the bag, the solution has been adopted
whereby the net has the highest tensile strength possible, great coverage
ability, a rib quality or slight rigid structure so that, once full, it
maintains its dimensional shape at rest, avoiding the typical flaccidity
of conventional bags, while also being very lightweight.

[0028] In order to achieve the foregoing ideal conditions for the plastic
net to be used in the applications mentioned above, the solution has been
adopted whereby maximum tensile strength is conferred to a synthetic
plastic net obtained through extrusion while also reducing, as much as
possible, the thickness of said net.

[0029] According to the preceding solution, the method of this invention
has been developed, wherein a synthetic plastic material with a reticular
tubular structure is obtained continuously through extrusion, is
subjected through hot drawing to a two-dimensional molecular orientation
operation in the longitudinal and transverse directions, is flattened,
and is then subjected to a calender operation to even out the thickness
of the flattened synthetic plastics material with a reticular oriented
structure.

[0030] A characteristic of the method of the invention is that the tubular
shaped synthetic plastics material with a reticular tubular structure is
arranged like a rope in the operation of molecular orientation of said
material by drawing it in the longitudinal and transverse directions, and
afterwards, the material is arranged in a tubular flattened shape to be
laminated by a calendering machine.

[0031] Another characteristic of the method of the invention is
constituted by the fact that a synthetic plastics material with a
reticular, tubular structure and obtained through extrusion, is hot
subjected to a molecular orientation operation through longitudinal
drawing, and to a transversal drawing operation by widening to give it
the shape of a reticular tubular flattened structure, which is subjected
to an operation to equal the thicknesses of the synthetic plastics
material, while the widened condition of said reticular tubular structure
is maintained, by laminating it and making it pass through a calendering
machine, to convert the reticular tubular flattened structure into a new
reticular tubular flattened and laminated structure.

[0032] Another characteristic of the invention lies in the fact that the
reticular tubular flattened structure can be cut on its two edges after
the longitudinal drawing operation and the transversal drawing by
widening operation, to convert it into two independent reticular laminar
structures, each laminated separately to form a reticular laminated
structure.

[0033] Another characteristic of the invention, along the same lines as
above, is the fact that the reticular tubular flattened structure can be
cut along an eccentric longitudinal line, after the longitudinal drawing
operation and the transverse drawing by widening operation, to convert it
into a reticular laminar structure double the width of the reticular
tubular flattened structure at the beginning, which is laminated across
its full width.

[0034] The invention comprises a plant for developing the preceding method
which, essentially, comprises an extrusion die for extruding a tubular
net structure made from synthetic thermoplastic material followed
sequentially by a two-dimensional hot drawing of said rope-like reticular
tubular structure using a longitudinal drawing device and a transversal
widening device for the same reticular tubular flattened structure, now
with a tubular flattened shape, followed finally by a laminating device
consisting of a calendering machine that shapes the said reticular
tubular flattened structure into a new reticular tubular flattened and
laminated structure.

[0035] Another characteristic of the plant of the invention is the fact
that the laminating device consists of a calendering machine with two
cylinders, with an adjustable reach and thermally conditioned, which at
the entrance has a widening device for widening the reticular structure
with a tubular flattened shape.

[0036] Another characteristic of the plant of the invention is that the
widening device for widening the reticular tubular flattened structure
consists of a triangular curvilinear plate that is mounted in a floating
manner inside the tubular reticular structure and does not reach the
motorised calendering rollers, and therefore it is retained within said
structure thanks to two idle rollers mounted on said triangular
curvilinear plate that roll on two idle rollers which, in turn, roll on
said tubular reticular structure which moves forward towards the
motorised rollers of calendering machine.

[0037] Another characteristic of the plant of the invention lies in the
fact that a longitudinal cutting device is arranged on each of the two
edges of the reticular tubular flattened structure, which are located
between the idle rollers and two pre-laminating rollers upstream from the
rollers of calendering machine.

[0038] Another characteristic of the plant of the invention is the fact
that in one case a single eccentric longitudinal cutting device for
cutting the reticular tubular flattened structure is provided, said
cutting device being complemented with an opening/turning device located
between the pre-laminating rollers and the calendering rollers.

[0039] The invention comprises the reticular structure material resulting
from the preceding method, which has the characteristic of consisting of
a synthetic plastic shaped according to a reticular filiform structure
wherein, having a tubular flattened shape, the filaments making up the
sides of the net mesh of said structure and the crossover points of said
filaments for shaping the net, have the same common thickness.

[0040] Another characteristic of the material of the invention lies in the
fact that the thickness of the crossover points of the net filaments is
equal to the thickness of the filaments making up the sides of the net
that are not affected by the laminating action through a calender and, in
some cases, the thickness of the crossover points on the net and the
thickness of the sides thereof is smaller than the thickness of the sides
of the net before being affected by the laminating process through a
calender.

[0041] Finally a characteristic of the invention is also the fact that the
reticular structure of the net is monolith and obtained through extruding
a synthetic plastics material susceptible to having the characteristics
of an elastomer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to facilitate the understanding of the foregoing ideas, a
method is described below for shaping a reticular material, a plant for
performing said method and a material resulting from said method, all
according to the invention and with reference to the illustrative
accompanying drawings, in which:

[0043]FIG. 1 is a schematic supposed elevation view of the development of
the stages for shaping a reticular material, performed according to the
method of the invention.

[0044] FIG. 2 is a schematic supposed plane view of the development of the
stages for shaping a reticular material, performed according to the
method of the invention.

[0045]FIG. 3 is a plane, geometrically schematic view of a fragment of
material with an ideal reticular structure wherein the sides of the
meshes are regularly rectilinear and their crossover points are
represented by flared projections.

[0047]FIG. 5 is a geometrically schematic perspective view of a cross on
the sides of four meshes in FIG. 3, once the material with a reticular
structure has been laminated according to the thickness of the sides
thereof.

[0049]FIG. 7 is a plane view of a fragment of a conventional extruded net
with squared mesh, which can only have one molecular orientation.

[0050] FIG. 8 is a perspective view of a part of the fragment of the net
with squared mesh in the preceding figure, showing in relief the
crossover points of the sides of the mesh.

[0051] FIG. 9 is a perspective view of the part of the net with squared
mesh in the preceding figure, once the mesh crossover points have
undergone a laminating operation.

[0052] FIG. 10, similar to FIG. 7, is a plane view of a fragment of an
extruded net with rhomboid shape mesh, which can only have one molecular
orientation.

[0053] FIG. 11 is a perspective view of a part of the fragment of net with
rhomboid shaped mesh in the preceding figure, showing in relief the
crossover points of the sides of the mesh.

[0054]FIG. 12, similar to FIG. 9, is a perspective view of the part of
the net in the preceding figure once the crossover points have undergone
a laminating operation.

[0055] FIG. 13 is a schematic view of a tubular net extrusion plant to
which there is connected a plant for drying the extruded net and
performing a longitudinal molecular orientation, followed by a laminating
calender for laminating the net arranged transversally and a winding
apparatus for the laminated net.

[0056] FIG. 14 is a schematic view of a plant intended for obtaining an
extruded tubular net followed by longitudinal drawing for its molecular
orientation and by laminating in a calender which ends in winding up the
net.

[0057] FIG. 15 is a schematic view of a plant intended for the transverse
orientation of an extruded tubular net, which can be oriented, or not, in
the longitudinal direction.

[0058] FIG. 16 is a schematic view, according to an upper view, of a
calendering head for widening the flattened tubular net and immediately
laminating it.

[0059] FIG. 17 is a schematic, sectional view along line XVII-XVII of FIG.
16, in a side elevation view, distinguishing the device for widening or
pressing the flattened tubular net, located at the entrance to the
laminating calender.

[0060] FIG. 18 is a schematic view of a section along line XVIII-XVIII in
FIG. 16.

[0061]FIG. 19 is a schematic, centred longitudinal sectional elevation
view, showing the device for widening or pressing a tubular flattened
net, and the sectioning of the edges thereof and their separation into
two reticular laminar structures that are fed separately into respective
laminating calendering machines.

[0062] FIG. 20 is a schematic, centred longitudinal sectional elevation
view, showing the device for widening or pressing a tubular flattened
net, and the sectioning of one of the two edges thereof and its opening
into a reticular laminar structure double the width of the tubular
flattened net at the beginning, which is fed into a laminating
calendering machine.

[0063] FIG. 21 is a comparative graph of the strength and elongation of
two tubular nets, one standard type and the other one laminated according
to the invention.

[0064]FIG. 22 is a comparative graph of the strength per unit weight of
two tubular nets, one standard type and the other one laminated according
to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0065] The method that is the object of this invention, which consists
essentially in a synthetic plastics material with a reticular tubular
structure being hot subjected to a two-dimensional molecular orientation
operation, in the longitudinal and transverse directions, through
drawing, followed by an operation to equal the thicknesses of the
synthetic plastics material through laminating it in a calender, is shown
graphically in the diagrams in FIGS. 1 and 2.

[0066]FIG. 1 shows what is supposedly a side elevation view, of the
development of the stages for shaping a thermoplastic material with a
reticular tubular structure 1, obtained in this tubular shape from an
extrusion die 2, from which extrusion die 2 it is gathered in the form of
a rope 3 between two rotary entry rollers 4 that deliver it to two other
rotary drawing rollers 5 that have a greater angular speed that the
former ones, whereby longitudinal drawing occurs that determines the
molecular orientation of the material with a reticular tubular structure
1, which determines the increased tensile strength thereof.

[0067] Then, when exiting the rotary drawing rollers 5 the rope-like 3
material with a reticular tubular structure 1 is introduced into a
widening device 6 wherein said rope 3 opens and is arranged as a
reticular flattened tubular structure 7 and it is immediately fed in
between two rotary pressing rollers 8 which laminate the material with a
reticular tubular structure 1 between them, in order to convert it into a
material with a reticular tubular laminated structure 9 having a reduced,
constant thickness, which has also undergone a molecular orientation in
the transverse direction.

[0068] FIG. 2 shows a top view of the development of the stages for
shaping the thermoplastic material with a reticular, tubular structure 1,
showing the same components as the previous figure, indicating the
function thereof which is not evident in said previous figure.

[0069]FIG. 3 shows in a geometrically schematic view, a fragment of a
material with a reticular structure 1 which, it is established, has not
been laminated, wherein the mesh, which is squared, is made up of
regularly rectilinear sides 10 that cross over regularly forming
crossover points 11 that are thicker than sides 10 and are shown as
noticeably lenticular flared projections. FIG. 4 shows a side view of
said flared projections according to a section along line IV-IV in FIG.
3.

[0070]FIG. 5 is a schematic perspective view of the material with a
reticular structure 1A in FIG. 3 once it has undergone a laminating
operation by calendering to flatten the flared projections of crossover
points 11, reducing them to disc-shaped crossover points 12 having a
thickness equal to the diameter of sides 10 of the squared mesh. FIG. 6
shows a side view of said disc-shape crossover points 12 according to a
section along line VI-VI in FIG. 5.

[0071]FIG. 7 shows a fragment of a material with a reticular structure
and a real shape and which is defined as a conventional extruded net 13
with squared mesh which has an assumed two-dimensional molecular
orientation, and has mesh formed by the orthogonal intersection of
filaments that form the sides 14 thereof and establish relevant crossover
points 15, which are relevant with respect to said filaments owing to the
increased thickness resulting from the sum of the thicknesses thereof in
the crossover points of said filaments of sides 14 of the mesh, with the
relief thereof being visible in the perspective view of part of said
extruded net 13, forming FIG. 8. FIG. 9 shows the part of extruded net
13A in FIG. 8, once it has undergone a laminating operation, wherein it
is observed that the thickness of the relevant crossover points 15 in the
mesh, indicated in said FIG. 8, has reduced with respect to the thickness
of sides 14 of the mesh thereof, creating flat crossover points 16.

[0072] FIG. 10, similar to FIG. 7, shows a fragment of a material with a
reticular structure and real shape and which is defined as a conventional
extruded net 17 with rhomboid mesh, which has an assumed two-dimensional
molecular orientation, and has rhomboid mesh formed by the intersection
of filaments forming sides 18 thereof and that establish relevant
crossover points 19, designated as such for the same reasons as those
given above in FIG. 8, with the relief thereof being visible in the
perspective view of part of said extruded net 17, forming FIG. 11. FIG.
12 shows the portion of extruded net 17A in FIG. 10, once it has
undergone a laminating operation, wherein it is observed that the
thickness of the relevant crossover points 19 of the mesh, indicated in
said FIG. 11, has been reduced with respect to the thickness of sides 18
of the mesh thereof, creating flat crossover points 20.

[0073] FIG. 13 shows a plant for developing the method of the invention
which in practice is disregarded, which comprises, essentially, an
extrusion machine 21 which, using a rotary die 22, produces a material
with a reticular structure in the shape of a conventional type extruded
tubular net 23, which extruded tubular net 23 is cooled in a vat
containing water and led to a plant 24 that shakes it and from which it
passes to a molecular orientation plant 25, comprising a pair of
motorised entry rollers 26, a heated air tunnel 27 and a pair of
motorised exit rollers 28 that rotate faster than the previous pair, from
which the extruded tubular oriented net 23A is forwarded to a widening
device 29 and to a laminating head made up of a pair of motorised
calender rollers 30, at the exit of which the extruded, flattened,
oriented and laminated net 23B is gathered on a winding apparatus 31.

[0074] FIG. 14 corresponds to another possible plant for performing the
method of the invention, which, as above, is disregarded in practice, and
which like the plant described in FIG. 13, comprises extruding machine 21
and rotary die 22 from which there emerges the material with a reticular
structure in the shape of a conventional type tubular extruded net 23,
which is led to a longitudinal drawing device that is made up of a pair
of traction rollers 32 for said tubular extruded rope-like net 23, where
with said rollers lying on a retention drum 33, the lower roller applies
said rope against a large part of the periphery of said retention drum 33
from which it is separated by a guiding roller 34 which leads it in the
vertical direction towards a driver roller 35, immersed in the bath in a
vat 36, through which there circulates the tubular structured net 23
until it reaches another driver roller 35 that sends it to a guiding
roller 37 that is applied to a drawing drum 38 from which it passes to a
driver drum 39 and, then, to a pair of traction rollers 40, which deliver
the oriented material to motorised rollers 30 in a calendering machine,
which material is then gathered onto a winding apparatus 41.

[0075] FIG. 15 corresponds to a plant designed for the transverse
orientation of the material with a reticular structure, which is
preferably applied to transversal widening of laminar material, without
excluding the possibility of being applied, with lower effectiveness, to
a tubular material. The plant consists of a conventional machine in the
textile industry for treating fabrics widthways, which are known by the
name of tenters 43 and which comprises a tunnel provided with heating
means through which there extend two chains that have needles that move
parallel to one another.

[0076] FIGS. 16, 17 and 18 show a schematic view of an embodiment of the
means for widening and laminating the material with a reticular tubular
structure, that comprises a widening device 29 made up of a triangular
curvilinear plate 44 that is assembled in a floating state, but retained,
inside the tubular reticular structure 23A (see FIG. 13) and between two
idle rollers 45 that rotate on said tubular reticular structure 23A
allowing it to advance towards motorised rollers 30 of the calendering
machine, while retaining said widening device 29 thanks to two rollers 46
thereof that prevent the triangular curvilinear plate 44 from passing
between idle rollers 45.

[0077] The top motorised roller 30 is mounted in a pivoting frame 47
which, by means of micrometric screws allows the reach between the two
motorised rollers to be varied in order to adjust the pitch between them
to the thickness desired for laminating the material with a reticular
structure 23A.

[0079]FIG. 19 shows an embodiment of the invention according to which the
widening device 29 or pressing device, which is housed inside a tubular
flattened net 7, allows the edges of said net to be sectioned by a
cutting device 51 and separated into two reticular laminated structures
7A and 7B which are fed together between a pair of pre-laminating rollers
52 and, immediately, they are fed separately into respective laminating
calendering machines 30A from which there emerge two reticular laminated
structures 9A and 9B.

[0080] FIG. 20 shows another embodiment of the invention according to
which the widening device 29 or pressing device, which is housed inside a
tubular flattened net 7, allows one of the two edges of said net to be
sectioned by a cutting device 51, before it passes between two
pre-laminating rollers 52, and to be extended in the transverse direction
by an opening/turning device 53 to adopt the shape of a reticular laminar
structure 7C double the width of the tubular flattened structure 7 at the
beginning, which is fed into a laminating calendering machine 30A from
which there emerges a reticular laminated structure 9C.

[0081] As an example of the behaviour of a standard material with a
reticular tubular structure and non-oriented rhomboid mesh, and a
laminated material with a reticular tubular structure and oriented
rhomboid mesh, both materials consisting of a two-thread mesh, the weight
of the first one material, per square meter, is 54 g, and the weight of
the second one, per square meter, is 37 g, with the characteristics of
absolute resistance according to the elongation being those indicated in
FIG. 21, whereas their resistance per weight unit is indicated in FIG.
22. In both cases, the graphs of said figures have been drawn up on the
basis of tests conducted using the INSTRON 4301 testing apparatus,
wherein the probes are 250 mm wide, the distance between the clamps is 50
mm, and the traction speed 500 mm/min.

[0082] In view of FIGS. 21 and 22 it is noted that the material with a
reticular tubular structure that underwent the two-dimensional molecular
orientation and laminating operations is more resistant than the standard
material, even though it has a smaller weight, and it must take into
account that the normal working conditions do no exceed elongation values
over 5%, as otherwise the mesh would become deformed, all as detailed in
the following table:

[0083] With the tubular laminated mesh described in this invention
practical improvements are obtained that overcome the drawbacks detailed
at the beginning of the description suffered by the other types of mesh
and films, and with a reticular structure or mesh that is the object of
this invention, it is possible to combine the advantages of the mesh
described in the previous paragraphs, while also overcoming their
drawbacks.

[0084] Since this mesh originates from a tubular extruded net, and it is
oriented in the longitudinal and transverse directions (bi-oriented), it
has a high degree of resistance for all kinds of loads. As the threads
and knots are flattened, the mesh looses a fair part of its rigidity and
so it occupies less space when it is removed and, moreover, owing to its
fullness a large number of metres can be wound on an individual spool.
Since it is not a woven mesh, there is no waste in the form of loose
threads when said mesh is cut to dismantle the pallets and, consequently,
the problem of dirt in the rear pallet parts and forklift trucks is
avoided. Another important advantage is that, depending on the materials
used and the drawing ratio applied, the mesh can have higher elasticity,
which greatly facilitates its application.

[0085] The tubular, two-dimensionally oriented and laminated mesh that is
described in the invention has a good resistance-weight ratio, as it
originates from an extruded oriented mesh, whereby it is possible to
obtain low cost packaging. It has good dimensional stability, and so the
packaging obtained with this mesh maintains its vertical shape and offers
a clear view of the message printed on the film band. Since the threads
and knots, formed by the intersections between them, are flattened, this
mesh provides a better product coverage factor and, for the same reason,
a greater number of metres can be wound on the spools than with extruded,
non-oriented mesh.